Direct smelting process

ABSTRACT

A process for direct smelting a metalliferous feed material is disclosed. The process includes the steps of partially reducing metalliferous feed material and substantially devolatilising coal in a pre-reduction vessel and producing a partially reduced metalliferous feed material and char. The process also includes direct smelting the partially reduced metalliferous feed material to molten metal in a direct smelting vessel using the char as a source of energy and as a reductant and post-combusting reaction gas produced in the direct smelting process with pre-heated air or oxygen-enriched air to a post-combustion level of greater than 70% to generate heat required for the direct smelting reactions and to maintain the metal in a molten state.

The present invention relates to a process for producing molten metal(which term includes metal alloys), in particular although by no meansexclusively iron, from a metalliferous feed material, such as ores,partly reduced ores and metal-containing waste streams, in ametallurgical vessel containing a molten bath.

The present invention relates particularly to a molten metal bath-baseddirect smelting process for producing molten metal from a metalliferousfeed material.

A process that produces molten metal directly from a metalliferous feedmaterial is generally referred to as a “direct smelting process”.

One known direct smelting process, which is generally referred to as theRomelt process, is based on the use of a large volume, highly agitatedslag bath as the medium for smelting top-charged metal oxides to metaland for post-combusting gaseous reaction products and transferring theheat as required to continue smelting metal oxides. The Romelt processincludes injection of oxygen-enriched air or oxygen into the slag via alower row of tuyeres to provide slag agitation and injection of oxygeninto the slag via an upper row of tuyeres to promote post-combustion. Inthe Romelt process the metal layer is not an important reaction medium.

Another known group of direct smelting processes that is slag-based isgenerally described as “deep slag” processes. These processes, such asDIOS and AISI processes, are based on forming a deep layer of slag with3 regions, namely: an upper region for post-combusting reaction gaseswith injected oxygen; a lower region for smelting metal oxides to metal;and an intermediate region which separates the upper and lower regions.As with the Romelt process, the metal layer below the slag layer is notan important reaction medium.

Another known direct smelting process, which relies on a molten metallayer as a reaction medium and is generally referred to as the HIsmeltprocess, is described in International application PCT/AU96/00197 (WO96/31627) in the name of the applicant.

The HIsmelt process as described in the International applicationcomprises:

(a) forming a molten bath having a metal layer and a slag layer on themetal layer in a vessel;

(b) injecting into the bath:

(i) a metalliferous feed material, typically metal oxides; and

(ii) a solid carbonaceous material, typically coal, which acts as areductant of the metal oxides and a source of energy; and

(c) smelting the metalliferous feed material to metal in the metallayer.

The HIsmelt process also comprises post-combusting reaction gases, suchas CO and H₂, released from the bath in the space above the bath withoxygen-containing gas and transferring the heat generated by thepost-combustion to the bath to contribute to the thermal energy requiredto smelt the metalliferous feed material.

The HIsmelt process also comprises forming a transition zone above thenominal quiescent surface of the bath in which there are ascending andthereafter descending droplets or splashes or streams of molten metaland/or slag which provide an effective medium to transfer to the baththe thermal energy generated by post-combusting reaction gases above thebath.

An object of the present invention is to provide an improved directsmelting process.

According to the present invention there is provided a process fordirect smelting a metalliferous feed material which includes the stepsof:

(a) supplying metalliferous feed material and coal to a pre-reductionvessel;

(b) partially reducing metalliferous feed material and substantiallydevolatilising coal in the pre-reduction vessel and producing apartially reduced metalliferous feed material and char;

(c) supplying the partially reduced metalliferous feed material and charproduced in step (b) to a direct smelting vessel;

(d) supplying pre-heated air or oxygen-enriched air to the directsmelting vessel; and

(e) direct smelting the partially reduced metalliferous feed material tomolten metal in the direct smelting vessel using the char as a source ofenergy and as a reductant and post-combusting reaction gas produced inthe direct smelting process with the pre-heated air or oxygen-enrichedair to a post-combustion level of greater than 70% to generate heatrequired for the direct smelting reactions and to maintain the metal ina molten state.

The process is particularly, although by no means exclusively, relevantto medium and high volatile coals. Medium volatile coals are understoodherein to mean coals containing 20-30 wt % volatiles. High volatilecoals are understood herein to mean coals containing in excess of 30 wt% volatiles.

In the case of medium and high volatile coals, the basis of the presentinvention is the realisation that substantial devolatilisation of thesecoal types prior to introducing the coal into a direct smelting vesselmakes it possible to operate economically a direct smelting process atpost-combustion levels of 70% or more using heated air oroxygen-enriched air as the oxygen-containing gas for post-combustion.

Preferably step (b) produces partially reduced metalliferous feedmaterial having a pre-reduction degree of less than 65%.

Preferably, the oxygen concentration in the oxygen-enriched air is lessthan 50 vol. percent.

The term “substantially devolatilising” means removal of at least 70 wt.percent of the volatiles from coal.

The term “post-combustion” is defined as:$\frac{\left\lbrack {CO}_{2} \right\rbrack + \left\lbrack {H_{2}O} \right\rbrack}{\left\lbrack {CO}_{2} \right\rbrack + \left\lbrack {H_{2}O} \right\rbrack + \lbrack{CO}\rbrack + \left\lbrack H_{2} \right\rbrack}$

where:

[CO₂]=volume % of CO₂ in off-gas;

[H₂O]=volume % of H₂O in off-gas;

[CO]=volume % of CO in off-gas; and

[H₂]=volume % of H₂ in off-gas.

The term “off-gas” is defined herein as gas generated by smeltingreactions and post-combustion and prior to optional addition of anyfurther carbonaceous feed material such as natural gas into that gas.

Preferably the process includes pre-heating air or oxygen-enriched airfor step (d) to a temperature in the range of 800-1400° C. andthereafter supplying the pre-heated air or oxygen-enriched air to thedirect smelting vessel in step (d).

More preferably the temperature is in the range of 1000-1250° C.

Preferably the process includes using off-gas discharged from the directsmelting vessel as a source of energy for pre-heating air oroxygen-enriched air prior to supplying the heated air or oxygen-enrichedair to the direct smelting vessel in step (d).

Preferably the process includes cooling the off-gas discharged from thedirect smelting vessel prior to using the off-gas as the energy source.

Preferably the process includes using part of the off-gas dischargedfrom the pre-reduction vessel as a source of energy for pre-heating airor oxygen-enriched air prior to supplying the heated air oroxygen-enriched air to the direct smelting vessel in step (d).

Preferably the process includes pre-heating the air or oxygen-enrichedair in one or more than one hot blast stove.

Preferably the process includes pre-heating the metalliferous feedmaterial prior to step (a) of supplying the metalliferous feed materialto the pre-reduction vessel.

Preferably the process includes pre-heating the metalliferous feedmaterial using off-gas discharged from the pre-reduction vessel.

Preferably the pre-reduction vessel is a fluidised bed.

More preferably the process includes recycling off-gas discharged fromthe fluidised bed back to the fluidised bed.

Preferably the process includes recycling at least 70% by volume of theoff-gas discharged from the fluidised bed back to the fluidised bed.

The term “fluidised bed” is understood herein to include both bubblingand circulating types. Combination bubbling and circulating are alsoincluded.

The term “metalliferous feed material” is understood herein to mean anymetalliferous feed material, which includes metal oxides, such as ores,partly reduced ores and metal-containing waste streams.

Step (e) may be any suitable direct smelting process.

Preferably step (e) includes direct smelting the partially reducedmetalliferous feed material in accordance with the HIsmelt process whichincludes:

(a) forming a molten bath having a metal layer and a slag layer on themetal layer in the direct smelting vessel;

(b) injecting the metalliferous feed material and the char into themetal layer via a plurality of lances/tuyeres;

(c) smelting the metalliferous feed material to molten metalsubstantially in the metal layer;

(d) causing molten metal and slag to be projected as splashes, droplets,and streams into a space above a nominal quiescent surface of the moltenbath and forming a transition zone; and

(e) injecting the pre-heated air or oxygen-enriched air into the directsmelting vessel via one or more than one lance/tuyere andpost-combusting reaction gases released from the molten bath, wherebythe ascending and thereafter descending splashes, droplets, and streamsof molten metal and slag in the transition zone facilitate heat transferto the molten bath, and whereby the transition zone minimises heat lossfrom the vessel via the side wall in contact with the transition zone.

The term “metal layer” is understood herein to mean a region or zonethat is predominantly metal. Specifically, the term covers a region orzone that includes a dispersion of molten slag in a metal continuousvolume.

The term “quiescent surface” in the context of the molten bath isunderstood herein to mean the surface of the molten bath under processconditions in which there is no gas/solids injection and therefore nobath agitation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described further by way of example withreference to the accompanying drawings, of which:

FIG. 1 is a flow sheet, in largely schematic form, of the process of thepresent invention; and

FIG. 2 is a vertical section through a preferred form of a directsmelting vessel for use in the process shown in FIG. 1.

The description of the preferred embodiment shown in FIG. 1 is in thecontext of producing iron from iron ore. However, it is noted that thepreferred embodiment is equally applicable to producing metals(including metal alloys) from other metalliferous feed material.

With reference to FIG. 1, iron ore is pre-heated in pre-heat cyclones103,105 to a temperature of the order of 750° C. and is transferred to afluid bed reactor 107 which operates at a temperature of the order of800-1000° C. Coal (typically, medium and/or high volatile coal), oxygen,and a reducing gas which includes high levels of CO and H₂ are alsosupplied to the reactor 107. The pre-heated iron ore is partiallyreduced in the reactor 107 to a pre-reduction degree that preferably isless than 65% and the coal is substantially devolatilised and formschar. The term “pre-reduction degree” in this context means thepercentage of oxygen removed assuming a starting point of Fe203 andassuming Fe is 100% pre-reduction.

The off-gas discharged from the reactor 107 is transferred through thepre-heat cyclones 103,105 and pre-heats the iron ore supplied to thesecyclones. The off-gas is then cooled in a venturi scrubber 108. Thecooled off-gas is split into two streams. One stream, which is at least70% of the total volume of off-gas, is supplied to a CO₂ scrubber 110,reheated and then returned as the reducing fluidising gas to the reactor107. The other stream is supplied to hot blast stoves 109 and used ascombustion gas which heats the stoves.

The partially reduced iron ore and char from the reactor 107, which aretypically at temperatures of the order of 600-900° C., and airpre-heated to a temperature of the order of 1200° C. from the stoves 109are supplied to a direct smelting vessel 111.

The partially reduced iron ore is smelted to molten iron in the vessel111 and reaction gases, such as CO and H2 produced in smelting thepre-reduced iron ore are post-combusted to a post-combustion level of atleast 70%. The heat generated by post-combustion is used to maintaintemperatures within the vessel 111.

A portion of the off-gas discharged from the vessel 111 is transferredvia a venturi scrubber 113 to the stoves 109 and is used as a combustiongas which contributes to heating the stoves 109.

The direct smelting process operating in the direct smelting vessel 111may be any suitable process.

The preferred direct smelting process is the HIsmelt process asdescribed in general terms hereinafter with reference to FIG. 2 and inmore detail in International application PCT/AU99/00538 in the name ofthe applicant. The disclosure in the patent specification lodged withthe International application is incorporated herein by cross-reference.

The preferred direct smelting process is based on:

(a) forming a molten bath having a metal layer and a slag layer on themetal layer in the direct smelting vessel 111;

(b) injecting the partially reduced iron ore and the char (andoptionally other carbonaceous material, such as additional coal) intothe metal layer via one or more than one lance/tuyere;

(c) smelting the partially reduced iron ore to molten iron substantiallyin the metal layer;

(d) causing molten material to be projected as splashes, droplets, andstreams into a space above a normal quiescent surface of the molten bathand forming a transition zone; and

(e) injecting the pre-heated air or oxygen-enriched air into the directsmelting vessel 111 via one or more than one lance/tuyere andpost-combusting reaction gases released from the molten bath to apost-combustion level of greater than 70% and generating gas phasetemperatures of the order of 2000° C. or higher in the transition zone,whereby the ascending and thereafter descending splashes, droplets andstreams of molten metal and slag in the transition zone facilitate heattransfer to the molten bath, and whereby the transition zone minimisesheat loss from the vessel via the side walls in contact with thetransition zone.

The direct smelting vessel 111 may be any suitable vessel.

The preferred direct smelting vessel is the vessel described in generalterms hereinafter with reference to FIG. 2 and in more detail inInternational application PCT/AU99/00537 in the name of the applicantand the disclosure in the patent specification lodged with theInternational application is incorporated herein by cross-reference.

The vessel 111 shown in FIG. 2 has a hearth that includes a base 3 andsides 55 formed from refractory bricks; side walls 5 which form agenerally cylindrical barrel extending upwardly from the sides 55 of thehearth and which include an upper barrel section 51 and a lower barrelsection 53; a roof 7; an outlet 9 for off-gases; a forehearth 57 fordischarging molten metal continuously; a forehearth connection 71 thatinterconnects the hearth and the forehearth 57; and a tap-hole 61 fordischarging molten slag.

In use, under steady-state process conditions, the vessel 111 contains amolten bath of iron and slag which includes a layer 15 of molten metaland a layer 16 of molten slag on the metal layer 15. The arrow marked bythe numeral 17 indicates the position of the nominal quiescent surfaceof the metal layer 15 and the arrow marked by the numeral 19 indicatesthe position of nominal quiescent surface of the slag layer 16. The term“quiescent surface” is understood to mean the surface when there is noinjection of gas and solids into the vessel.

The vessel 111 also includes 2 solids injection lances/tuyeres 11extending downwardly and inwardly at an angle of 30-60° to the verticalthrough the side walls 5 and into the slag layer 16. The position of thelances/tuyeres 11 is selected so that the lower ends are above thequiescent surface 17 of the metal layer 15 under steady-state processconditions.

In use, under steady-state process conditions the partially reduced ironore and the char from the reactor 107 (and optionally other carbonaceousmaterial, such as coal), and fluxes (typically lime and magnesia)entrained in a carrier gas (typically N₂) are injected into the metallayer 15 via the lances/tuyeres 11. The momentum of the solidmaterial/carrier gas causes the solid material and gas to penetrate themetal layer 15. Carbon partially dissolves into the metal and partiallyremains as solid carbon. The iron ore is smelted to metal and thesmelting reaction generates carbon monoxide gas. The gases transportedinto the metal layer 15 and generated via smelting produce significantbuoyancy uplift of molten metal, solid carbon, and slag (drawn into themetal layer 15 as a consequence of solid/gas/injection) from the metallayer 15 which generates an upward movement of splashes, droplets andstreams of molten metal and slag, and these splashes, and droplets, andstreams entrain slag as they move through the slag layer 16.

The buoyancy uplift of molten metal, solid carbon and slag causessubstantial agitation in the metal layer 15 and the slag layer 16, withthe result that the slag layer 16 expands in volume and has a surfaceindicated by the arrow 30. The extent of agitation is such that there isreasonably uniform temperature in the metal and the slagregions—typically, 1450-1550° C. with a temperature variation of no morethan 30° in each region.

In addition, the upward movement of splashes, droplets and streams ofmolten metal and slag caused by the buoyancy uplift of molten metal,solid carbon, and slag extends into the top space 31 above the moltenmaterial in the vessel and:

(a) forms a transition zone 23; and

(b) projects some molten material (predominantly slag) beyond thetransition zone and onto the part of the upper barrel section 51 of theside walls 5 that is above the transition zone 23 and onto the roof 7.

In general terms, the slag layer 16 is a liquid continuous volume, withgas bubbles therein, and the transition zone 23 is a gas continuousvolume with splashes, droplets, and streams of molten metal and slag.

The vessel Ill further includes a lance 13 for injecting the pre-heatedair or oxygen-enriched air from the stoves 9 into the vessel 111. Thelance 13 is centrally located and extends vertically downwardly into thevessel. The position of the lance 13 and the gas flow rate through thelance 13 are selected so that under steady-state process conditions theoxygen-containing gas penetrates the central region of the transitionzone 23 and maintains an essentially metal/slag free space 25 around theend of the lance 13.

In use, under steady-state process conditions, the injection of theoxygen-containing gas via the lance 13 post-combusts reaction gases COand H₂ to a post-combustion level of greater than 70% in the transitionzone 23 and in the free space 25 around the end of the lance 13 andgenerates high gas phase temperatures of the order of 2000° C. or higherin the gas space. The heat is transferred to the ascending anddescending splashes droplets, and streams, of molten material in theregion of gas injection and the heat is then partially transferred tothe metal layer 15 when the metal/slag returns to the metal layer 15.

The free space 25 is important to achieving high levels of postcombustion because it enables entrainment of gases in the space abovethe transition zone 23 into the end region of the lance 13 and therebyincreases exposure of available reaction gases to post combustion.

The combined effect of the position of the lance 13, gas flow ratethrough the lance 13, and upward movement of splashes, droplets andstreams of molten metal and slag is to shape the transition zone 23around the lower region of the lance 13—generally identified by thenumerals 27. This shaped region provides a partial barrier to heattransfer by radiation to the side walls 5.

Moreover, under steady-state process conditions, the ascending anddescending droplets, splashes and streams of metal and slag is aneffective means of transferring heat from the transition zone 23 to themolten bath with the result that the temperature of the transition zone23 in the region of the side walls 5 is of the order of 1450° C.-1550°C.

The vessel 111 is constructed with reference to the levels of the metallayer 15, the slag layer 16, and the transition zone 23 in the vessel111 when the process is operating under steady-state process conditionsand with reference to splashes, droplets and streams of molten metal andslag that are projected into the top space 31 above the transition zone23 when the process is operating under steady-state operatingconditions, so that:

(a) the hearth and the lower barrel section 53 of the side walls 5 thatcontact the metal/slag layers 15/16 are formed from bricks of refractorymaterial (indicated by the cross-hatching in the figure);

(b) at least part of the lower barrel section 53 of the side walls 5 isbacked by water cooled panels 8; and

(c) the upper barrel section 51 of the side walls 5 and the roof 7 thatcontact the transition zone 23 and the top space 31 are formed fromwater cooled panels 58, 59.

Each water cooled panel 8, 58, 59 (not shown) in the upper barrelsection 51 of the side walls 5 has parallel upper and lower edges andparallel side edges and is curved so as to define a section of thecylindrical barrel. Each panel includes an inner water cooling pipe andan outer water cooling pipe. The pipes are formed into a serpentineconfiguration with horizontal sections interconnected by curvedsections. Each pipe further includes a water inlet and a water outlet.The pipes are displaced vertically so that the horizontal sections ofthe outer pipe are not immediately behind the horizontal sections of theinner pipe when viewed from an exposed face of the panel, ie the facethat is exposed to the interior of the vessel. Each panel furtherincludes a rammed refractory material which fills the spaces between theadjacent horizontal sections of each pipe and between the pipes. Eachpanel further includes a support plate which forms an outer surface ofthe panel.

The water inlets and the water outlets of the pipes are connected to awater supply circuit (not shown) which circulates water at high flowrate through the pipes.

Many modifications may be made to the preferred embodiment describedabove without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. A process for direct smelting a metalliferousfeed material comprising: (a) supplying metalliferous feed material andcoal to a fluidized bed; (b) partially reducing metalliferous feedmaterial and substantially devolatilizing coal in the fluidized bed andproducing a partially reduced metalliferous feed material and char; (c)supplying the partially reduced metalliferous feed material and charproduced in step (b) to a direct smelting vessel; (d) using off-gasdischarged from the fluidized bed as a source of energy and pre-heatingair or oxygen-enriched air and thereafter supplying the pre-heated airor oxygen-enriched air to the direct smelting vessel; and (e) directsmelting the partially reduced metalliferous feed material to moltenmetal in the direct smelting vessel using the char as a source of energyand as a reductant and post-combusting reaction gas produced in thedirect smelting process with the pre-heated air or oxygen-enriched airto a post-combustion level of greater than 70% to generate heat requiredfor the direct smelting reactions and to maintain the metal in a moltenstate.
 2. The process defined in claim 1 wherein the oxygenconcentration in the oxygen-enriched air is less than 50 vol. percent.3. The process defined in claim 1 including pre-heating air oroxygen-enriched air for step (d) to a temperature in the range of800-1400° C. and thereafter supplying the pre-heated air oroxygen-enriched air to the direct smelting vessel in step (d).
 4. Theprocess defined in claim 3 wherein the temperature is in the range of1000-1250° C.
 5. The process defined in claim 3 including using off-gasdischarged from the direct smelting vessel as a source of energy forpre-heating air or oxygen-enriched air prior to supplying the heated airor oxygen-enriched air to the direct smelting vessel in step (d).
 6. Theprocess defined in claim 3 including pre-heating the air oroxygen-enriched air in one or more than one hot blast stove.
 7. Theprocess defined in claim 1 including recycling at least part of theoff-gas discharged from the fluidized bed back to the fluidized bed. 8.The process defined in claim 7 including recycling at least 70% byvolume of the off-gas discharged from the fluidized bed back to thefluidized bed.
 9. The process defined claim 1 wherein step (e) includes:(i) forming a molten bath having a metal layer and a slag layer on themetal layer in the direct smelting vessel; (ii) injecting themetalliferous feed material and the char into the metal layer via aplurality of lances/tuyeres; (iii) smelting the metalliferous feedmaterial to molten metal substantially in the metal layer; (iv) causingmolten metal and slag to be projected as splashes, droplets, and streamsinto a space above a nominal quiescent surface of the molten bath andforming a transition zone; and (v) injecting the pre-heated air oroxygen-enriched air into the direct smelting vessel via one or more thanone lance/tuyere and post-combusting reaction gases released from themolten bath, whereby the ascending and thereafter descending splashes,droplets, and streams of molten metal and slag in the transition zonefacilitate heat transfer to the molten bath, and whereby the transitionzone minimizes heat loss from the vessel via a side wall in contact withthe transition zone.
 10. The process defined in claim 1 furtherincluding injecting coal into the direct smelting vessel, whereby thecoal acts as a source of energy and as a reductant in the vessel.
 11. Aprocess for direct smelting a metalliferous feed material comprising:(a) supplying metalliferous feed material and medium or high volatilecoal to pre-reduction vessel comprising a fluidized bed; (b) partiallyreducing metalliferous feed material and substantially devolatilizingcoal in the pre-reduction vessel and producing a partially reducedmetalliferous feed material and char; (c) supplying the partiallyreduced metalliferous feed material and char produced in step (b) to adirect smelting vessel; (d) using off-gas discharged from thepre-reduction vessel as a source of energy and pre-heating air oroxygen-enriched air and thereafter supplying the pre-heated air oroxygen-enriched air to the direct smelting vessel; and (e) directsmelting the partially reduced metalliferous feed material to moltenmetal in the direct smelting vessel using the char as a source of energyand as a reductant and post-combusting reaction gas produced in thedirect smelting process with the pre-heated air or oxygen-enriched airto a post-combustion level of greater than 70% to generate heat requiredfor the direct smelting reactions and to maintain the metal in a moltenstate.
 12. The process as claimed in claim 11, wherein the oxygenconcentration in the oxygen-enriched air is less than 50 vol. percent.13. The process as claimed in claim 11 including pre-heating air oroxygen-enriched air for step (d) to a temperature in the range of800-1400° C. and thereafter supplying the pre-heated air oroxygen-enriched air to the direct smelting vessel in step (d).
 14. Theprocess as claimed in claim 13 wherein the temperature is in the rangeof 1000-1250° C.
 15. The process as claimed in claim 11 including usingoff-gas discharged from the direct smelting vessel as a source of energyfor pre-heating air or oxygen-enriched air prior to supplying the heatedair or oxygen-enriched air to the direct smelting vessel in step (d).16. The process as claimed in claim 13 including pre-heating the air oroxygen-enriched air in one or more than one hot blast stove.
 17. Theprocess as claimed in claim 11 including recycling at least part of thegas discharged from the fluidized bed back to the fluidized bed.
 18. Theprocess defined in claim 17 including recycling at least 70% by volumeof the off-gas discharged from the fluidized bed back to the fluidizedbed.
 19. The process defined in claim 11 wherein step (e) includes: (i)forming a molten bath having a metal layer and a slag layer on the metallayer in the direct smelting vessel; (ii) injecting the metalliferousfeed material and the char into the metal layer via a plurality oflances/tuyeres; (iii) smelting the metalliferous feed material to moltenmetal substantially in the metal layer; (iv) causing molten metal andslag to be projected as splashes, droplets, and streams into a spaceabove a nominal quiescent surface of the molten bath and forming atransition zone; and (v) injecting the pre-heated air or oxygen-enrichedair into the direct smelting vessel via one or more than onelance/tuyere and post-combusting reaction gases released from the moltenbath, whereby the ascending and thereafter descending splashes,droplets, and streams of molten metal and slag in the transition zonefacilitate heat transfer to the molten bath, and whereby the transitionzone minimizes heat loss from the vessel via the side wall in contactwith the transition zone.
 20. The process defined in claim 11 furtherincluding injecting coal into the direct smelting vessel, whereby thecoal acts as a source of energy and as a reductant in the vessel.